Ten thousand kiloliters of soy sauce a year, the way Hiroshi Futamura figures it. Getting out his calculator, he quickly converts the number, pausing to make sure he's got the right translation: "2.6 million gallons."

Even by Japanese standards, that's a lot of shoyu.

But that's what will be rolling off the bottling line at Kikkoman's newly dedicated 100,000-square-foot plant in Folsom. The facility, which Futamura manages, is the final link between the samurai-era origins of the Japanese company and the high-tech present of the California food industry.

Two million gallons of shoyu -- the Japanese term for soy sauce -- a large number on its own, becomes even more impressive because soy sauce is not something that's easily gulped down. It's drizzled out by the spoonful, perhaps in a little ceramic dish alongside sushi, or mixed into noodle broth or miso soup. Maybe a little more if it's in a marinade.

Kikkoman sees a growing market for soy sauce in this country, especially on the West Coast, where Asian culinary influences are strong.

The company picked Folsom for its new plant because of its relative proximity to California's major urban areas and its comparatively low land and labor costs. But Folsom has something else even more important to the production of soy sauce: a steady supply of clear, high- quality water flowing from the American River into Folsom Lake.

Good water is critical to soy sauce-making, just as it is to brewing beer or sake. In all three fermentation processes, highly mineralized water can ruin the product. Anheuser-Busch, which makes Budweiser, located its enormous brewery 60 miles away in Fairfield in part because the company secured rights to clear, low-mineral water straight out of Lake Berryessa.

The Folsom facility, which resembles a brewery with its intricate snake of pneumatic tubes and its rows of stainless steel tanks, is Kikkoman's second U.S. manufacturing plant -- but it is the first in a quarter century. Kikkoman opened its first U.S. facility in Walworth, Wis., in 1973. Kikkoman picked Walworth because of its proximity to the soybean and wheat fields of the Midwest. The new Folsom plant will use the same prized soybeans from Illinois and wheat from the Dakotas.

It's five to six months from the wheat and soybean harvest to the final sauce. Once in the plant, the soybeans and wheat are heated and puffed like breakfast cereal. The two are combined with hot water and seed starter in a culturing process known as koji, which results in flavor-packed enzymes. Next, brine is added, and the whole mash -- known as shikomi -- ferments. The properly fermented mash is pressed and turned into unrefined soy sauce, which is aged and pasteurized before being bottled. As with any fermentation process, temperature control and cleanliness are critical.

Shoyu is believed to have originated in China. According to some accounts, the recipe was brought to Japan in the 13th century by Kakushin, a Zen priest.

Kikkoman's roots go back to the 1600s, when Hyozaemon Takanishi, an ancestor of the current part-owners, began making shoyu in Noda, north of Tokyo.

Kikkoman assumed its present corporate form in 1917, and today is the world's dominant shoyu company, with annual revenues in excess of $1 billion. Unfortunately, what's bottled in Folsom -- 2.6 million gallons notwithstanding -- will take some time to reach California supermarket shelves. The first batch must ferment and age for several months, but then the resulting brew will only be poured into five-gallon pails for local restaurants and food service operations. Consumers will have to wait, but eventually Kikkoman plans to bottle the shoyu in the familiar 10 5/8- and 20-ounce bottles. Then patient Northern California consumers can taste for themselves what lured Kikkoman to the banks of the American River.

PRODUCERS CALL CALIFORNIA HOME

Kikkoman joins a number of Japan-based food firms with facilities in Northern California.

Four companies are making sake -- Takara in Berkeley (ShoChiku Bai brand), Gekkeikan in Folsom, Ozeki in Hollister and Hakusan in Napa -- and all are open to visitors.

The Hakusan brewery, located at 1 Executive Way in Napa near the junction of highways 29 and 12, is probably the most visible to tourists. It's open 10 a.m.-5 p.m. Thursday- Tuesday and has a self-guided tour and a tasting room. (707) 258-6160. Takara Sake, 708 Addison St., Berkeley, offers tasting but no tours. It's open noon to 6 p.m. daily. (510) 540-8250.

Hakusan is part of Kohnan International, which includes Williams Rice Milling (Tamaki brand rice, both medium-grain and short-grain koshihikari varieties) and Silverado Hills Cellars (which markets wine domestically and internationally).

A Japanese company owns Markham Vineyards, north of St. Helena. Other Japanese-owned food companies in the region include Salad Cosmo of Dixon, which grows bean sprouts for distribution in the Bay Area and Sacramento; Shoei, in the Yuba City area, which dries prunes for shipment to Japan; and INA in Bakersfield, a Japanese-owned farm growing citrus fruit.

HOLD THE SOY SAUCE, PLEASE

Want to see a Japanese host squirm? Just take a bowl of steaming, white, Japanese-style short-grain rice and douse it with a few splashes of soy sauce.

This is the first thing many Americans do when they receive a bowl of rice in a Japanese restaurant. But in Japan, it's considered poor table manners, the sort of childish habit that mothers discourage and something you're supposed to give up when you switch from eating with a spoon to using chopsticks.

Representatives of Kikkoman, who naturally want their American customers to use soy sauce in any way they're comfortable doing so, declined to comment on this matter of etiquette. But ask any Japanese mother -- she'll set you straight.